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The present invention relates to application specific integrated circuits (xe2x80x9cASICsxe2x80x9d) operating with Advanced Microcontroller Bus Architecture (xe2x80x9cAMBAxe2x80x9d), and more particularly to an application specific integrated circuit having an on-chip bridge for connection to off-chip devices.
As their name implies, application specific integrated circuits, or ASICs, are essentially integrated circuits implemented on a chip designed for a specific use or application. ASICs are used for numerous applications. For instance, ASICs are used for machine-to-machine communications for the space shuttle, for DVD processing, for advanced digital signal processing, for trans-oceanic cables, etc. Such special purpose processors can be embedded in essentially any equipment to enhance and control its functions.
Typically an ASIC includes one or more core processors, memory and other functional devices on a single semiconductor chip. Having the devices on the same chip allows data to be easily and quickly transferred between the various devices on the chip. To accommodate high speed data transfers on a chip, specialized bus protocols have been developed specifically for this purpose. For example, ARM Limited, a company specializing in the design of processor cores, has developed one such protocol known as the Advanced Microcontroller Bus Architecture, or AMBA. AMBA includes the Advanced High-performance Bus, or AHB, which provides for high-speed transfers of data between various components on a chip.
As one might expect, development of an ASIC is a complicated and expensive process. Once a design has been completed to the point of actual production of a new device, i.e. putting the design on silicon, it is often too late to make changes. Any corrections or additions of new functions essentially require a new design and are therefore very expensive.
It is common, however, for customers to request the addition of new functions to existing ASICs. To assist in redesigning an ASIC to meet these requests, it would be very desirable to have the capability of connecting an external device to the ASIC with the new or additional function for testing purposes. Allowing external testing of proposed redesigns would greatly reduce work and time to implement additions to an ASIC versus having to produce ASICs incorporating the proposed redesigns on the chip. Moreover, in some cases, it may be more cost effective to improve an existing ASIC by simply adding such an external device instead of redesigning the ASIC. To effectively do external testing or additions however, the external device would need to connect into the ASIC""s system bus to exchange data. This can be a problem, however, because many external devices, for example field programmable gate arrays, do not operate at the speed of the ASIC""s system bus, i.e. the AMBA AHB, and are therefore incompatible with the AMBA AHB.
In accordance with the present invention, an ASIC is provided having an AMBA AHB and a bridge to provide a data transfer link to off-chip devices. The bridge includes a logic section and a buffer section. The logic section includes clock division and modification of control signals to allow the high speed AHB to communicate with a slower speed off-chip device or bus. The logic section also includes registers to hold signals being transferred by the bridge in order to accommodate differing clock rates. The buffer section provides conversion of signal voltage levels between the core voltages and the voltage levels required off-chip.